A disc drive typically includes a rigid housing or deck supporting a disc stack assembly and an actuator, among other components. The disc pack assembly includes one or more discs that are rotated by a spindle motor during drive operations. Using read/write devices positionable by the actuator assembly, data is read from and written to tracks on a disc surface.
Ideally, the tracks would be circular with its center coincidental with the axis of rotation of the spindle motor. However, in reality, various factors contribute to track mis-registration or overall run-out, resulting in tracks that deviate from the ideal. Understandably, such error can have an adverse impact on the overall performance of the disc drive.
Significant contribution to track misregistration or overall run-out can come from a behavior commonly referred to as “disc flutter”—a phenomenon where the disc is deformed in vibrational motion such that it no longer presents a flat plane for the writing or reading of data. This behavior can be especially problematic at high spindle motor speeds, and needs to be addressed if overall disc drive performance is to be improved.
It is understood that as the disc rotates, air around the disc surfaces is dragged into motion. A substantial portion of the air or other gaseous fluid near the axis of rotation spins in nearly solid body rotation along with the disc pack. Nearer to the outer edges of the discs, however, the surrounding fluid is pumped away from the disc pack assembly by centrifugal forces. Yet other fluid flow streams are generated whereby they flow between adjacent discs towards the inner edges of the discs. Collectively, turbulent flow around the disc pack assembly induces disc flutter and provokes excitation of the read/write heads, thus contributing to track mis-registration and overall run-out, among other problems.
Earlier work to reduce disc flutter has been directed towards providing as extensive a shroud as possible around the disc pack. A shroud can be generally described as a surface substantially transverse to the disc surface and circumscribing the disc pack assembly. The shroud therefore prevents air from flowing off the outer edges of the discs and thereby promotes laminar flow behavior in the vicinity of the disc pack assembly.
In addition to promoting less turbulent fluid flow around the disc pack assembly, a shroud is sometimes used to reduce or maintain the power requirements of the spindle motor. When fluid is allowed to flow out from the vicinity of the disc pack assembly, replacement fluid flows into the vicinity of the disc pack assembly. A certain amount of energy would be expended by the spindle motor to bring this replacement fluid up to speed. Therefore, if fluid can be prevented from flowing out of the disc pack assembly in the first place, for example, by use of a shroud, less energy and a lower power requirement for the spindle motor would be needed.
It would appear, however, that with some disc drive configurations, simply providing an extensive shroud may not offer sufficient improvement because significant run-out issues remain. Clearly, the interplay of the surrounding fluid with a rotating disc pack assembly and read/write devices suspended in the fluid flow creates several challenging issues, of which only a few have been described above. The task of finding a practicable solution to these and other problems is complicated by the fact that much remains to be learnt of windage issues, and that care must be taken not to create new problems while trying to solve existing ones.
Therefore, there remains a need for better solutions to these and other problems. The present invention attempts to satisfy such a need while at the same time offer additional advantages over the prior art.